These materials are formed by nanoparticles coated in a matrix.
The term “nanoparticles” is understood to mean particles, generally solid particles, the size of which is between 1 nm and a few hundred nanometers. For example, the size of the nanoparticles in question may be between 1 nm and 200 nm.
Nanostructured composite materials have properties that are radically different from those of the same material in the solid state, in particular as a function of the size of the nanoparticles coated in the matrix.
For example, it is generally necessary to provide nanoparticles with a size of less than 10 nm in order to modify the electronic and chemical properties of this material. According to another example, it is generally necessary to have nanoparticles with a size of less than 100 nm in order to modify the mechanical properties of the material (toughness, hardness, plasticity, etc.).
There are various techniques for forming such materials on a target surface.
One of these consists in coupling two different systems, one for depositing the nanoparticles on the target surface, the other for depositing the matrix on this target surface, in which matrix the nanoparticles are intended to be coated.
One device for synthesizing a nanostructured composite material belonging to this technique is proposed in the article “Ferromagnetic, Transparent and Conducting ITO-Fe-Cluster Composite Films”, D. L. Peng & al., IEEE Transactions on Magnetics, vol. 41, no. 10, pp. 3406 to 3408, October 2005.
In this article, the device mainly comprises three regions: a first region formed by a sputtering chamber, a second region in which the nanoparticles grow and the size of which can be controlled and a third region formed by a deposition chamber in which the synthesis of the material is carried out.
The first two regions can be likened to a first system for the deposition of the nanoparticles on the target surface.
The third region is comparable to a second system for depositing the matrix, which is located in the synthesis chamber.
The coupling between the two systems is carried out by means of a skimmer through which the nanoparticles can enter into the synthesis chamber in order to be deposited on the target surface. This skimmer makes it possible to maintain a pressure differential between the two systems that it separates in order to facilitate the entry of the nanoparticles into the synthesis chamber.
The first system comprises means for generating a jet of carrier gas conveying the nanoparticles. Specifically, these means comprise a sputtering chamber for generating the nanoparticles and a source of carrier gas, such as argon.
The sputtering chamber in this case uses a plasma-gas-condensation (PGC) technique.
The sputtering chamber comprises an extension in which the nanoparticles thus generated can grow.
The first system also comprises an intermediate chamber, connected to the sputtering chamber by a skimmer. Once generated, the jet of carrier gas conveying the nanoparticles then exits the sputtering chamber, crosses the intermediate chamber and finally enters into the synthesis chamber, in order to enable the deposition of the nanoparticles on the target surface. The intermediate chamber thus comprises a skimmer at the inlet and a skimmer at the outlet, in order to maintain a high pressure differential between the sputtering chamber and the synthesis chamber.
For this purpose, the pressure in the intermediate chamber is lower than the pressure in the sputtering chamber. The pressure in the synthesis chamber is also lower than the pressure in the intermediate chamber.
For this reason, this device cannot use just any type of system for the deposition of the matrix. Indeed, this device must use sputter deposition with a special cathode of “Helicon” type, enabling operation at very low pressure. In this case, the pressure in the synthesis chamber is maintained at 0.013 Pa.
The device disclosed in this article has several limitations.
A first limitation is linked to the fact that the pressure must decrease from the sputtering chamber to the synthesis chamber so that the jet of carrier gas can convey the nanoparticles to the target surface located in the synthesis chamber.
This means that the pressure in the synthesis chamber is very low.
This very low pressure in the synthesis chamber is the cause of a second limitation. This is because the use of specific sputter deposition, of “Helicon” type, in order to be able to deposit the matrix at very low pressure in the synthesis chamber is obligatory.
A third limitation is linked to the source of nanoparticles, which functions via plasma gas condensation. Specifically, this technique is only possible for metallic nanoparticles. In this article, the nanoparticles are made of iron.
A fourth limitation is linked to the structure of the nanostructured composite material finally synthesized. Specifically, this article provides sequential structures where zones that contain nanoparticles and zones that do not contain any thereof follow one another. It is not therefore envisaged to synthesize nanostructured composite materials in which the nanoparticles are distributed homogeneously in the matrix.